1. Field of the Invention
This invention relates generally to devices for the acquisition of electroencephalographic (EEG) signals, and more particularly concerns an EEG electrode and an EEG electrode locator assembly that can be applied by a user in combination with an EEG electrode locator headgear without assistance, for acquiring high quality EEG signals.
2. Description of Related Art
Advances in detection and characterization of electroencephalographic (EEG) signals from the brain have allowed EEG monitoring to be useful in analysis of neurological and sleep disorders, and laboratory studies of vigilance. Recent advances have, for example, provided much information about the correlation between EEG signals and an individual""s level of arousal, in a continuum from vigilance to drowsiness, and sleep onset. Shifts in EEG signals have been directly correlated with changes in performance, particularly during tasks which require sustained attention over prolonged periods of time. Devices for monitoring EEG signals are typically used in a laboratory environment or in a home for sleep studies, but are typically set up and operated by trained technicians. However, application of EEG monitoring to environments for study and monitoring of brain performance, such as for monitoring brain activity in the home, office, aircraft cockpit, and train or truck operations cabins, for example, has been severely hampered by cumbersome detection and recording equipment, and the need for the assistance of a technician typically required to obtain high quality data.
In fitting EEG electrodes to the scalp of a subject being monitored, an EEG technician will typically first measure the distances between the nasium and the occipital bone, and between the mastoid processes, to identify the top center (Cz) of the head, and will then position all other electrodes relative to these landmarks to comply with the International 10/20 System that is well known in the art as the standard for positioning of EEG electrodes. The technician will then part the hair of the scalp of the subject at the intended electrode sites, clean the electrode sites to remove dirt, hair oil, and the like, and prepare the scalp to remove the top layer of dead skin, to ensure that scalp-electrode impedance values of less than 5 kxcexa9 are obtained. The minimum level of impedance needed to minimize EEG artifact is dependent, in part, on the quality of the EEG amplifiers. Filtering certain environmental noises, such as 60 Hz interference, allows acceptable EEG signals to be acquired with impedance levels up to 100 kxcexa9. Other artifacts are magnified as the impedances increase unless the signal acquisition equipment has been designed to minimize these effects. For example, replacing a conventional EEG system which uses wires to transmit non-amplified EEG to the data acquisition/storage unit with a system that amplifies and digitizes the signals on the head will help to reduce movement artifacts. Maintaining sufficient downward pressure on an electrode with higher impedance values will minimize the contribution of artifacts resulting from the electrode sliding across hair or the scalp.
Conventionally, after preparation of the intended electrode sites on the scalp, electrodes are glued to the scalp with collodion, typically a viscous solution of pyroxilin, a commercially available nitrocellulose, in ether and alcohol, that is a particularly noxious preparation that can bond with the scalp and hair, to provide a stable scalp-electrode interface, until dissolved by a solvent such as acetone, or a non-acetone, oil based collodion remover.
A variety of hats, caps, helmets and headgear are known that have been developed to position EEG electrodes according to the International 10/20 System and provide a scalp-electrode interface without the use of an adhesive such as collodion. However, these types of devices still require technician assistance in the preparation of the electrode site, and are commonly uncomfortable and unacceptable for use during activities of work and daily living. One such sleep monitoring headgear utilizes a circumferential elastic headband to generate an electrode seating pressure for a single electrode located at the top center of the head of a subject. It has been found, however, that when such a circumferential elastic headband is utilized to seat multiple electrodes, the headband slides up and posteriorly on the forehead.
Such conventional hats, caps, helmets and headgear also typically make it difficult for a user to part the hair or abrade their scalp at the electrode site without assistance. For example, most of the electrode caps require a technician to abrade the scalp with a blunt tipped syringe and then inject conductive gel into the electrode embedded into the cap. Another conventional device requires the technician to lift or turn a disposable electrode on its side after a conductive gel on the electrode has made contact with the hair of the scalp, in order to part the hair at the intended area of the scalp for placement of the electrode. Several systems intended for use in the laboratory for non-ambulatory EEG monitoring dispense electrode gel to the electrode, but would make an EEG electrode locator headgear uncomfortably heavy and inconvenient for ambulatory use outside a laboratory environment. Another type of device utilizes sharp tipped metal points to penetrate the dead layer of skin. However, such sharp metal points can pose a medical danger due to the potential for infection, particularly with repeated abrasions, and the possibility of penetration of the skull if the device were to be struck accidentally during ambulatory activity, or other activities during daily living.
It would therefore be desirable to provide an EEG electrode and an EEG electrode locator assembly for use in combination with an EEG electrode locator headgear that allows the user to apply the electrodes at the electrode sites, permitting conventional scalp preparation techniques to be applied by the user without technical assistance. The present invention meets these needs.
Briefly, and in general terms, the present invention provides for an EEG electrode and an EEG electrode assembly for use in combination with an EEG electrode locator headgear for a user that allows the user to locate and apply the EEG electrodes accurately according to the International 10/20 System without technical assistance, to allow the acquisition of high quality EEG signals. The EEG electrode locator headgear is of the type that is portable and comfortable, allowing it to be worn by the user during daily activities as one would a cap or visor. The EEG locator headgear typically includes a plurality of locator straps connectable to one or more of the EEG electrode locators that form an electrode locator assembly with the EEG electrode for accurately positioning one or more of the EEG electrodes relative to the user""s scalp, and for biasing the plurality of electrodes toward the user""s scalp. Each EEG electrode is adapted to be received in and cooperate with a corresponding EEG electrode locator ring. Each EEG electrode includes a dispenser assembly adapted to dispense an electrically conductive gel through the user""s hair onto the user""s scalp. The dispenser assembly includes a base member for conducting EEG signals from the scalp of the user to a corresponding electrode locator ring for signal transmission to an EEG monitor.
The invention accordingly provides for an electroencephalograph (EEG) electrode locator assembly for use in combination with an EEG electrode locator headgear for accurate positioning of the EEG electrode locator assembly on the scalp of a user. In a presently preferred embodiment, the EEG electrode assembly comprises an EEG electrode locator member adapted to be mounted to EEG electrode locator headgear; and an EEG electrode received in and removably electrically coupled to the EEG electrode locator headgear. The EEG electrode includes an electrically conductive base adapted to be in electrical communication with the scalp of a user for detecting EEG signals of the user. The EEG electrode and the electrically conductive base member typically may be made from a carbon and ABS composite plastic material with a silver/silver chloride (Ag/AgCl) coating. The EEG electrode locator member also typically may be made from a carbon and ABS composite plastic material with a Ag/AgCl coating, although the EEG electrode locator member may alternatively be made from another similar suitable electrically conductive material, such as stainless steel, for example. In one presently preferred aspect, the EEG electrode locator member comprises an electrically conductive ring having a central opening adapted to receive the EEG electrode. The EEG electrode locator member also preferably has a surface defining a plurality of slots for receiving and connection to one or more locator straps. The EEG electrode locator headgear preferably includes an electrical connector, and the EEG electrode locator member includes means for connecting the electrical connector to the EEG electrode locator member. In a presently preferred aspect, the means for connecting the electrical connector to the EEG electrode locator member comprises an electrical terminal connector aperture, and terminal connector screw.
In another presently preferred aspect, the EEG electrode is disposable. The EEG electrode base also preferably includes a housing defining a chamber for containing and dispensing an electrically conductive gel, and the housing of the EEG electrode base has a surface defining a lower gel dispenser opening for dispensing the electrically conductive gel. A porous foam pad is also preferably attached to the EEG electrode base, by insertion of an upper annular flange of the foam pad into a corresponding annular groove of the electrode base. The porous foam pad provides padding for a comfortable scalp interface, absorbs the conductive gel to maintain a consistent volume of gel between the electrode base and scalp, and compresses with minimal downward pressure to minimize slide artifacts. The foam pad is easily disposable and replaceable, and is removably mounted to the EEG electrode base by a removable bottom connector ring. The bottom connector ring is removably received in a lower annular channel of the EEG electrode base which includes a plurality of inwardly projecting tabs that are received in a corresponding plurality of slots in the bottom connector ring. An annular groove or space is formed between the bottom connector ring and the housing of the EEG electrode base, with an edge portion of the porous foam pad removably received in the annular space, so that the porous foam pad can be removed from the EEG electrode base and replaced by another porous foam pad by removing and replacing the bottom connector ring.
The EEG electrode base housing also preferably includes an upper, outer radial flange, with a plurality of slots formed in the housing and the outer radial flange, and an outer radial groove connected to each of the slots in the housing, for receiving and mating with a corresponding plurality of inner mounting tabs on the electrode locator member, respectively, for removably coupling the EEG electrode to the EEG electrode locator member.
In a presently preferred aspect, the EEG electrode includes a flexible gel fill cap having an interior plunger portion for dispensing the conductive gel from the EEG electrode gel chamber. The flexible gel fill cap includes a lower outer radial flange mounted to the upper outer radial flange of the base, and the flexible gel fill cap preferably includes an upper gel fill port, through which the electrically conductive gel may be introduced into the EEG electrode gel chamber. In another presently preferred aspect, the flexible gel fill cap is formed of a flexible, resilient material, so that by inversion of the gel cap by application of downward pressure on the gel cap to exert a pump action, the gel cap dispenses the conductive gel from the EEG electrode gel chamber. In another aspect, the EEG electrode includes an upper cap allowing the EEG electrode to be gripped for seating of the EEG electrode in the EEG electrode locator member, and in a presently preferred aspect, the upper cap has a surface defining opposing outer indentations for gripping and turning the upper cap for seating of the EEG electrode in the EEG electrode locator member.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.